1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) device and more particularly to a liquid crystal type emitting material being capable of being horizontally oriented and having improved emitting efficiency and an OLED device including the same.
2. Discussion of the Related Art
Recently, requirement for flat panel display devices having small occupied area is increased. Among the flat panel display devices, an OLED device, which may be called to as an organic electroluminescent device, is widely introduced.
The OLED device emits light by injecting electrons from a cathode as an electron injection electrode and holes from an anode as a hole injection electrode into an emission compound layer, combining the electrons with the holes, generating an exciton, and transforming the exciton from an excited state to a ground state. A flexible substrate, for example, a plastic substrate, can be used as a base substrate where elements are formed. Since the OLED device does not require a backlight assembly, the OLED device has low weight and low power consumption. Moreover, the OLED device can be operated at a voltage (e.g., 10V or below) lower than a voltage required to operate other display devices. In addition, the OLED device is adequate to produce full-color images.
FIG. 1 is a schematic cross-sectional view of the related art OLED device.
As shown in FIG. 1, the OLED device includes a first substrate (not shown), a second substrate (not shown) and an organic emitting diode E between the first and second substrates.
The organic emitting diode E includes a first electrode 10, a second electrode 30 and an organic emitting layer 20. The first electrode 10 is formed of a material having a relatively high work function to serve as an anode. For example, the first electrode 10 may be formed of indium-tin-oxide (ITO). The second electrode 30 is formed of a material having a relatively low work function to serve as a cathode. For example, the second electrode 30 may be formed of aluminum (Al) or Al alloy.
To increase emission efficiency, the organic emitting layer 20 includes a hole injecting layer (HIL) 21, a hole transporting layer (HTL) 22, an emitting material layer (EML) 23, an electron transporting layer (ETL) 24 and an electron injecting layer (EIL) 25.
In the OLED device, the hole from the first electrode 10 as an anode is transferred into the emitting material layer 23 through the hole injecting layer 21 and the hole transporting layer 22, and the electron from the second electrode 30 as a cathode is transferred into the emitting material layer 23 through the electron injecting layer 25 and the electron transporting layer 24. The hole and the electron combines in the emitting material layer 23 to emit light.
For example, material in following Formula 1-1 or Formula 1-2 are used for the emitting material layer 23.

Referring again to FIG. 1, the materials are randomly arranged in the emitting material layer 23. The randomly arranged materials cause a limitation in the emitting efficiency, i.e., a limitation in brightness, and decrease of power consumption of the OLED device.